Once upon a time, a tiny photo-sharing app named Instagram came out of nowhere to trounce all the other photo-sharing apps — thanks to a helping hand from Twitter, which made it awfully easy for Instagram users to post their photos within 140-character missives. Twitter and Instagram's friendly relationship made sense: Instagram founder Kevin Systrom once interned for Twitter co-founder Evan Williams, and Twitter chairman Jack Dorsey was an early investor in the photo service.

But now the two internet services are no longer BFF — and the growing rift is bad news for users.

Today, Twitter announced that Instagram photos would soon no longer be viewable within tweets. Formerly, a user could click on an Instagram link to see that picture expanded inside a Twitter card. Now that link will take them directly to Instagram's website.

Systrom, speaking at the LeWeb technology conference, confirmed the news. "We've decided that right now, what makes sense is to direct our users to the Instagram website," said Systrom. "Obviously things change as a company evolves."

This is just the most recent chill in what's become an increasingly frosty relationship, says Mat Honan at Wired. In April, Instagram was bought by Twitter's key rival, Facebook. In July, Twitter changed its API policy, and Instagram users were no longer able to quickly grow their followings by importing their list of Twitter pals. Twitter is even rumored to be working on its own photo filter and sharing feature. Inevitably those moves "reduce interoperability and cleave the services further apart," says Honan — "no matter who comes out ahead, in each of these battles, the people who use and love both networks are the real and clear losers."

This is frustrating, says Matt Buchanan at BuzzFeed. "Everyone is a multitude on the internet: Facebook, Twitter, Tumblr, Instagram and whatever other thing we're on are all little bits of who we are or whatever we're choosing to project outward." These social networks approximate our real-world identities, which is why this seemingly minor annoyance makes it "jarring to think that these identities are actually becoming even more fragmented."

Well, "photo sharing continues to be a volatile battleground for social networking services," says Nick Bilton at TheNew York Times, and "given the potential advertising dollars at stake, the tensions will likely continue to grow." When Facebook acquired Instagram, the newly-purchased service said in a blog post that the deal "means we can now work together to evolve and build a better Instagram for everyone." Apparently, that "everyone" doesn't include Twitter.